The proposed research is a continuation of ongoing studies of the role of the cellular milieu in regulating neuronal growth and development. The studies will focus on the expression and function of cytokines in the nervous system and on mechanisms by which these factors regulate neuronal survival and development. Specifically these studies will: (1) Define the anatomic and temporal patterns of expression of Interleukin 7 (IL7), Interleukin 9 (IL9), and macrophage colony stimulating factor (CSF-1) In the rat brain. The cell types which express the factors will also be defined. 2. Similarly define the cell types expressing the receptors for IL7, IL9, and CSF-1, as well as the anatomic and temporal patterns of expression of these receptors in rat brain. 3. Define the effects of IL7, IL9, and CSF-1 in promoting neuronal survival, extension of neurites, and gene expression in cultures of embryonic brain. The phenotype of responsive neurons will be defined, and effects on neural nonneuronal cells will be determined. In a broader sense, these studies seek to define the role of intercellular communication in development and function of the nervous system. It is hoped that these studies may indicate biochemical loci where the therapeutic intervention in disease processes may lead to a return to normal neuronal function.